212 Type of Cell Lamination [CHAP. 



Plexiform Layer. 



This lamina may be slightly shallower and may contain a few less nerve cell elements, 

 but it does not differ markedly from the same layer in the " precentral " area. 



Layer of Small Pyramidal Cells. 



Morphologically the cells in this layer resemble those in the " precentral " area. A com- 

 parative cell count has not been made, but in the " intermediate " field a more closely packed 

 appearance suggests a numerical increase. 



Layer of Medium-sized Pyramidal Cells. 



There is no point of distinctive value to be noted concerning this layer. In the " inter- 

 mediate" field there is an apparent increase in depth but it carries little importance. 



External Layer of Large Pyramidal Cells. 



It is an interesting truth that throughout the " intermediate " cortex pyramidal cells are 

 to be found at this level, equal in size, similar as regards chromophilic elements, and as 

 strong in point of number as in the " precentral " area ; in fact the layer exhibits no feature 

 sufficiently distinctive to be made vise of in formulating a differential judgment between the 

 two fields. Topographic variations, however, have to be noted ; in that part immediately 

 bordering the " precentral " area, the cells are appreciably larger than they are towards the 

 opposite margin, and it may be added here, that the cells undergo some diminution in volume 

 as the area is descended. 



Although alike in these two subdivisions, the same cells constitute a reliable guide in 

 distinguishing this cortex from that of the more anteriorly-placed frontal convolutions, as well 

 as from that of other regions ; for with the exception of the " postcentral," the " visuo-psychic " 

 and the " auditory temporal " cortex, there is none accommodating cells of equal size and 

 number at this particular cortical level. And another feature peculiar to the ' intermediate " 

 and to the typical " precentral " cortex is that the cell constituents of this lamina strive to 

 preserve an equality in size, that is to say, they do not commingle with cells of smaller diameter 

 to the extent obtaining in most other parts of the brain. 



On comparing sections stained for nerve cells with sections which display the nerve fibres, 

 it may be observed that the chief or outer line of Baillarger occupies a level corresponding 

 identically with these large pyramidal cells, and there seems to be no doubt that extensions or 

 collaterals of the same elements augment the prominence of the line. 



Layer of Stellate Cells. 



In sections stained for nerve fibres there is a narrow pallid zone, immediately underlying 

 the outer line of Baillarger, which marks the position of the stellate lamina. But when we 

 come to examine sections treated for the demonstration of nerve cells, we find that this layer, 

 although easy to orientate, is poorly supplied with constituent elements, and therefore does 

 not appear as a composite line ; indeed, we can only say that between the large external 

 pyramidal cells and the deep layer of large pyramids, to be next referred to, there is a clear 



